J. Misiewicz

Effects of Si-rich oxide layer stoichiometry on the structural and optical properties of Si QD/SiO2 multilayer films

The effects of the stoichiometry of the Si-rich oxide (SRO) layer, O/Si ratio, on the structural and optical properties of SRO/SiO2 multilayer films were investigated in this work. SRO/SiO2 multilayer films with different O/Si ratios were grown by a co-sputtering technique, and Si quantum dots (QDs) were formed with post-deposition annealing. By transmission electron microscopy (TEM) and glancing incidence x-ray diffraction (GIXRD), it was found that the Si QD size decreases with increases in O/Si ratio. The photoluminescence (PL) spectrum varies with the O/Si ratio in band position, shape and intensity. In addition, it was observed that the absorption edge blue-shifts with increases in the O/Si ratio. The change in the absorption edge is consistent with strengthening quantum confinement effects in Si QDs, as indicated by TEM and GIXRD. The optical properties were also investigated by 2D photoluminescence excitation (2D-PLE) and lifetime measurements. The origin of emission and absorption is discussed based on the absorption, PL, 2D-PLE and decay time measurements.

Explanation of annealing-induced blueshift of the optical transitions in GaInAsN/GaAs quantum wells

This letter aims to describe the effect of rapid thermal annealing on a Ga0.64In0.36As0.99N0.01/GaAs single quantum well grown by molecular-beam epitaxy. This effect was investigated using both photoluminescence and photoreflectance. A blueshift of optical transitions and a change of character of the ground-state transition were observed after annealing. We show that this behavior can be explained by a combination of two annealing-induced effects: A change in the nearest-neighbor configuration of nitrogen atoms and a simultaneous change in the quantum well profile due to atom diffusion across the quantum well interfaces.

Photoreflectance evidence of multiple band gaps in dilute GaInNAs layers lattice-matched to GaAs

Dilute Ga1−xInxNyAs1−y∕GaAs quantum wells with high In-content, which are under compressive strain, have been shown previously to exhibit multiple band gaps, likely due to the presence of different nitrogen nearest-neighbor environments, i.e., N‐Ga4−mInm(0⩽m⩽4) short-range-order clusters. Here, photoreflectance (PR) measurements on lattice-matched dilute GaInNAs-on-GaAs layers with low indium and nitrogen content are reported, which give evidence that these layers also exhibit several distinct band gaps. These distinct band gaps, which were found to coexist, are associated with different nitrogen bonding configurations, as revealed by Raman spectroscopy. Thus, the metastable nature of GaInNAs seems to be a persistent intrinsic property, irrespective of strain and indium content. The annealing-induced blueshift of GaInNAs band gap energy, which is usually observed in this system, has been associated with the change in the intensity of PR resonances related to different N‐Ga4−mInm configurations.

Photoreflectance investigations of the energy level structure in GaInNAs-based quantum wells

In this paper, we present the application of photoreflectance (PR) spectroscopy to investigate the energy level structure of GaInNAs-based quantum wells (QWs). Series of single GaInNAs/GaAs QWs wit ...

Molecular beam epitaxy of GaBiAs on (311)B GaAs substrates

We report the growth by molecular beam epitaxy of GaBixAs1−x epilayers on (311)B GaAs substrates. We use high-resolution x-ray diffraction (HRXRD), transmission electron microscopy, and Z-contrast imaging to characterize the structural properties of the as-grown material. We find that the incorporation of Bi into the GaBiAs alloy, as determined by HRXRD, is sizably larger in the (311)B epilayers than in (001) epilayers, giving rise to reduced band-gap energies as obtained by optical transmission spectroscopy.

Stark effect in semiconductor quantum dots

A theory of the Stark effect in semiconductor quantum dots has been developed for the case of dominating polarization interaction of an electron and a hole with the nanocrystal surface. A shift of electron and hole quantum well levels in a nanocrystal in the interband absorption range in a uniform external electric field is determined by the quantum-confinement quadratic Stark effect. An electro-optical method is proposed, making it possible to estimate the characteristic quantum dot radius at which three-dimensional excitons can exist.

Influence of Annealing on Excitation of Terbium Luminescence in YAlO3 Films Deposited onto Porous Anodic Alumina

Terbium-doped yttrium-aluminum oxide films were synthesized by spin-on deposition on porous anodic alumina grown on a silicon wafer and annealed from 400 to 1100°C. An influence of the annealing temperature on the terbium photoluminescence (PL) was studied using two-dimensional PL excitation and time-resolved spectroscopy. Further, a comparison of thermal quenching data for the most intensive 5 D 4 → 7 F 5 luminescence band of Tb 3+ ions was performed for 10-300 K. From the resultant data, the mechanisms of Tb excitation and its dependence on the annealing conditions are proposed and discussed.

Enhancement of Green Terbium-Related Photoluminescence from Highly Doped Microporous Alumina Xerogels in Mesoporous Anodic Alumina

Strong enhancement of green photoluminescence (PL) from microporous alumina xerogels, highly doped with terbium (from 30 to 60 wt % as Tb 2 O 3 ), is reported. The regular structure of a 30 μm thick, mesoporous anodic alumina layer was exploited for spin-on deposition of the alumina xerogel in a single step. The green PL, associated with predominant 5 D 4 - 7 F 5 transitions, along with 5 D 4 7 F j , j = 3, 4, 5, 6 transitions of Tb 3+ , was found to increase with terbium concentration in the alumina xerogel. This effect is attributed to cross-relaxation. The thermal quenching of the green terbium-related emission does not exceed a factor of two within a temperature range from 10 to 300 K for any of the alumina xerogels confined in anodic alumina. Further, such quenching is much reduced with the rise of temperature compared with (i) Tb-doped titania xerogel, (ii) Tb-implanted thermally grown silicon dioxide film, and (iii) Tb-doped alumina xerogels fabricated onto monocrystalline silicon Thus, the terbium-doped structure comprising alumina xerogel/anodic alumina is proposed as a basis for green room-temperature luminescent images.

Photoluminescence from GaN nanopowder: The size effect associated with the surface-to-volume ratio

Nanosized GaN powder with the average grain size changing from ∼10to∼30nm has been obtained by combustion method with some modifications and its optical properties have been investigated by photoluminescence (PL). The GaN band-gap-related PL band at ∼3.4eV and surface-related PL bands centered at ∼2.0 and ∼2.8eV have been observed for this powder. The relative intensities between observed PL bands change in favor of the surface-related PL band with the decrease of the grain size. This phenomenon has been attributed to the change in the surface-to-volume ratio.

Interference effects in electromodulation spectroscopy applied to GaAs-based structures: A comparison of photoreflectance and contactless electroreflectance

In this letter, we show that the oscillation features (OFs) usually observed in photoreflectance (PR) spectra of GaAs-based structures grown on the n-type GaAs substrate below the GaAs fundamental gap could be eliminated completely by applying the contactless electroreflectance (CER) instead of PR. This finding confirms that the origin of OFs is the modulation of the refractive index in the sample due to the generation of additional carriers by the modulated pump beam. In the case of CER spectroscopy, any additional carriers are not generated during the modulation hence CER spectra are free of OFs. This advantage of CER spectroscopy is very important in investigations of all structures for which OFs are present in PR spectra. In order to illustrate this advantage of CER spectroscopy we show PR and CER spectra measured first for the GaAs epilayer and next for more complicated steplike GaInNAsSb∕GaNAs∕GaAs quantum well structures.